In a braking system for a train, it is usual to use a regenerative brake for energy saving or prevention of abrasion of brake pads. A regenerative brake is a type of electric brake that obtains a reverse driving force (braking force) by causing a motor to function as a power generator and also transfers the obtained power to other trains. When a regenerative brake is used, a command for the regenerative brake is given from an automatic train-driving device included in the train to an inverter. The inverter generates a torque which has been instructed for the motor according to vector control or the like. The power generated at the time of executing regenerative braking is supplied to other trains via overhead lines. However, in this case, when there is no load such as a train serving as a transfer destination or when there is a relatively small load, an overhead wire voltage becomes high. In this case, in order to prevent damage to devices due to an excessive increase in the overhead wire voltage, control is performed in order to reduce the braking force of the regenerative braking and curtail increase in the overhead wire voltage. A state in which the motor does not generate a torque as instructed as a result of such curtailment control is referred to as regeneration invalidation.
When regeneration invalidation occurs, the braking force may become insufficient, and therefore, there is a control called electropneumatic blending control for compensating for this insufficiency using an air brake, which is a type of mechanical brake. For example, Patent Literature 1 describes an example of electropneumatic blending control. Patent Literature 1 describes a brake control method for adopting a smaller of a brake torque command value and a calculated value of a regenerative braking force as a value of the regenerative braking force when compensating for a difference between the brake torque command value corresponding to a required total braking force and the regenerative braking force using an air brake.